[lkml]   [2012]   [Feb]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 22/73] union-mount: Add two superblock fields for union mounts [ver #2]
From: Valerie Aurora <>

Add two fields to struct super_block to support union mounts:

(*) s_union_lower_mnts

A pointer to a cloned vfsmount tree of all the lower (read-only) mounts
unioned with the topmost (read-write) vfsmount. These mounts may have
submounts which will also be unioned; hence we copy the entire vfsmount
tree, not just the root vfsmounts.

(*) s_union_count

The number of lower mounts unioned at the root of the file system. This
count is the maximum number of directories that will ever be unioned with
a single directory. We use it to allocate a union stack of the correct
size for each directory.

Original-author: Valerie Aurora <>
Signed-off-by: David Howells <>

include/linux/fs.h | 10 ++++++++++
1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index a014f0f..f19772c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1509,6 +1509,16 @@ struct super_block {
* free_vfsmnt() if MNT_HARD_READONLY is set.
int s_hard_readonly_users;
+ /* Root of the private cloned vfsmount tree of the read-only
+ * mounts in this union (set in topmost vfsmount only)
+ */
+ struct vfsmount *s_union_lower_mnts;
+ /* Number of layers in this union, not counting the topmost or
+ * submounts.
+ */
+ unsigned int s_union_count;

/* superblock cache pruning functions */

 \ /
  Last update: 2012-02-21 21:05    [W:0.266 / U:1.084 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site